Guide to Power Protection

Surge Protectors, Power Conditioners, and UPS Systems

A guide to the different types of power protection devices, with a focus on Uninterruptible Power Supplies (UPS), their types, and how to size them.
Author

Chuck Nelson

Published

October 18, 2025

1 Purpose

This document explains the importance of protecting computer systems from common power problems. It provides a guide to the different types of power protection devices, with a focus on Uninterruptible Power Supplies (UPS), how they work, and how to select the right one for a given system.

2 What You’ll Learn

By the end of this reading, you will be able to:

  • Differentiate between a basic surge protector and a UPS.
  • Identify the three main types of UPS systems (Standby, Line-Interactive, and Online).
  • Understand the difference between a UPS’s VA and Wattage ratings.
  • Explain why a “Pure Sine Wave” output is important for modern computer systems.

This reading maps to the following program and course learning outcomes:

  • Program Learning Outcomes (PLOs):
    • 6. Maintain environment: Selecting and deploying appropriate power protection is a key aspect of maintaining a reliable computing environment.
  • Course Learning Outcomes (CLOs):
    • 1. Identify hardware and basic network components: This guide focuses on the identification and selection of critical power protection hardware.
    • 4. Configure hardware and basic network components: Sizing and installing a UPS is a common configuration task for IT professionals.

This exercise will help you develop the following skills and knowledge, which align with the O*NET SOC Code 15-1232.00 for Computer User Support Specialists.

Learning Objective O*NET KSAs Technologies Used
Differentiate between power protection devices. Knowledge: Computers & Electronics
Skills: Reading Comprehension, Critical Thinking		 UPS, Surge Protectors
Select an appropriate UPS for a computer system. Knowledge: Computers & Electronics
Skills: Troubleshooting, Technology Design		 UPS

3 Why Power Protection Matters

The power from a wall outlet is not always stable. Problems like surges, sags, and blackouts can damage sensitive electronic components and cause data loss. Power protection devices are designed to sit between the wall outlet and your computer to shield it from these issues.

3.1 Level 1: The Surge Protector

A basic power strip is just an extension cord, but a surge protector adds a vital layer of defense. It contains Metal Oxide Varistors (MOVs) that absorb excess voltage during a power spike (a surge), sacrificing themselves to protect the connected equipment. Their protective capacity is measured in Joules; a higher rating means it can absorb more energy. Because MOVs wear out after absorbing a surge, surge protectors should be replaced periodically or after any major electrical event.

3.2 Level 2: The Uninterruptible Power Supply (UPS)

A UPS is the most critical piece of power protection hardware for any important computer system. It contains a battery that provides seamless backup power during a momentary sag (brownout) or a complete blackout.

How a UPS Works

At its core, a UPS contains a battery, a charger to keep the battery full, and an inverter to convert the battery’s DC power back into AC power for the computer to use. The key difference between UPS types is how and when that inverter is used.

Types of UPS Systems

  1. Standby (or Offline) UPS: The simplest and most common type. The PC runs directly off wall power until a problem is detected, at which point the UPS switches to battery power in a few milliseconds. Best for home or small office use.

  2. Line-Interactive UPS: A step up from Standby. This type includes a transformer that allows it to correct for minor voltage fluctuations (sags and surges) without switching to the battery. This saves battery life and is ideal for areas with frequent but minor power issues.

  3. Online (or Double-Conversion) UPS: The most advanced and expensive type. The computer always runs off the battery, which is constantly being recharged from the wall power. The inverter is always on, meaning there is zero transfer time in the event of a power failure. This provides the cleanest, most stable power and is used for critical servers and sensitive equipment.

UPS Waveforms: Simulated vs. Pure Sine Wave

When running on battery, a UPS must create its own AC power. Cheaper models produce a Simulated or Stepped Sine Wave. More expensive models produce a Pure Sine Wave, which is a clean replica of utility power.

  • Why it matters: Modern, high-efficiency computer PSUs often use a technology called Active Power Factor Correction (Active PFC). These PSUs can sometimes unexpectedly shut down when running on a simulated sine wave. For modern gaming PCs or workstations, a Pure Sine Wave UPS is strongly recommended to ensure compatibility.

Figure Figure 1 contrasts the smooth output of a true sine wave with the stepped approximation produced by many entry-level UPS units when they are running on battery power.

Figure 1: Simulated (stepped) sine wave compared to a pure sine wave.

4 Sizing a UPS: A Practical Guide

4.1 VA vs. Watts: Understanding the Ratings

  • Watts (W): The real power drawn by your components. This is the number you use to size your computer’s PSU.
  • Volt-Amperes (VA): The apparent power. This rating will always be higher than the Wattage rating due to a factor called the “power factor.” As a rule of thumb, the Wattage rating of a UPS is roughly 60% of its VA rating (e.g., a 1000VA UPS is rated for about 600W).

To size a UPS, always use the Wattage. Add up the power draw of your computer and your monitor, then choose a UPS with a Wattage rating that is at least 20-25% higher to give yourself a safety margin.

4.2 Calculating Load and Runtime

UPS manufacturers provide charts or online calculators to estimate runtime. The runtime depends entirely on the load. A 1000VA/600W UPS might run a 300W computer system for 10 minutes, but a 600W system for only 3 minutes. The goal is to have enough time for a graceful shutdown, not to continue working through a long outage.

5 Reflect and Review

ImportantReflection: 3-2-1

Now that you have reviewed this document, take a moment to reflect on your learning. In your Microsoft Teams Student Notebook, create a new page for this topic and write down the following:

  • 3 types of UPS systems.
  • 2 key ratings to check when buying a UPS.
  • 1 question you still have about sine waves.

This reflection is for your instructor to review and helps solidify your understanding of the concepts.

TipCheck on Learning

Test your understanding with the following questions. These questions provide retrieval practice and reinforce key concepts covered in this reading. In your Microsoft Teams Student Notebook, answer the following:

  1. What is the primary difference between a surge protector and a UPS?
  2. A user has a high-end gaming PC with a modern, efficient PSU. What type of waveform output should their UPS have?
  3. What is the main advantage of a Line-Interactive UPS over a Standby UPS?
  4. A computer and monitor have a combined power draw of 400 Watts. You are looking at a UPS rated for 900VA / 500W. Is this an appropriate choice? Why or why not?
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